Albuquerque M L, Leffler C W
The Laboratory for Research in Neonatal Physiology, Departments of Physiology and Biophysics and Pediatrics, University of Tennessee, Memphis, Tennessee, 38163, USA.
Proc Soc Exp Biol Med. 1998 Dec;219(3):226-34. doi: 10.3181/00379727-219-44336.
Hypocapnia produces cerebral vasoconstriction. The mechanisms involved in hypocapnia-induced elevation of vascular smooth muscle tone remain unclear. We addressed the hypothesis that, in cerebrovascular smooth muscle, increases in extracellular pH (pHo) cause increases in Ins(1,4,5)P3 and cytosolic calcium ([Ca2+]c). Superfused primary cultures of piglet cerebral microvascular smooth muscle cells were exposed to artificial CSF (aCSF) of control (pHo 7. 4, PCO2 36 mm Hg), metabolic alkalosis (pHo 7.7, PCO2 36 mm Hg), or respiratory alkalosis (pHo 7.7, PCO2 19 mm Hg). Intracellular pH (pHi) and [Ca2+]c were measured, using BCECF and fura-2, respectively, with dual wavelength spectroscopy. Ins(1,4,5)P3 was determined by a protein binding assay. Both metabolic and respiratory acidosis treatments increased pHi from the control value of about 7.2 to 7.35. Metabolic and respiratory alkalosis increased Ins(1,4,5)P3, as we showed previously. Metabolic and respiratory alkalosis increased [Ca2+]c about 80% and 110%, respectively. Neither Ins(1,4,5)P3 nor [Ca2+]c increased in cells treated with aCSF that produced control pHo with increased pHi (7.3). In contrast, when pHo increased (7.7), but pHi was maintained at control (7.2), Ins(1,4,5)P3 increased from 123 pmol/well to 307 pmol/well and [Ca2+]c increased 46%. However, the increase of [Ca2+]c was less than with either respiratory or metabolic alkalosis. Thus, hypocapnia-induced cerebral vasoconstriction could involve production of Ins(1,4,5)P3 with resultant elevation in [Ca2+]c. While the Ins(1,4,5)P3 signal appears to be dependent on an increase in extracellular pH, a role for intracellular pH cannot be completely excluded.
低碳酸血症会引起脑血管收缩。低碳酸血症导致血管平滑肌张力升高所涉及的机制仍不清楚。我们探讨了这样一个假说：在脑血管平滑肌中，细胞外pH值（pHo）升高会导致肌醇-1,4,5-三磷酸（Ins(1,4,5)P3）和胞质钙浓度（[Ca2+]c）升高。将原代培养的仔猪脑微血管平滑肌细胞进行灌流，分别暴露于对照人工脑脊液（aCSF，pHo 7.4，PCO2 36 mmHg）、代谢性碱中毒（pHo 7.7，PCO2 36 mmHg）或呼吸性碱中毒（pHo 7.7，PCO2 19 mmHg）环境中。分别使用BCECF和fura-2通过双波长光谱法测量细胞内pH值（pHi）和[Ca2+]c。通过蛋白质结合测定法测定Ins(1,4,5)P3。代谢性和呼吸性酸中毒处理均使pHi从约7.2的对照值升高至7.35。如我们之前所示，代谢性和呼吸性碱中毒会使Ins(1,4,5)P3升高。代谢性和呼吸性碱中毒分别使[Ca2+]c升高约80%和110%。在用产生对照pHo且pHi升高（7.3）的aCSF处理的细胞中，Ins(1,4,5)P3和[Ca2+]c均未升高。相反，当pHo升高（7.7）但pHi维持在对照水平（7.2）时，Ins(1,4,5)P3从123 pmol/孔增加到307 pmol/孔，[Ca2+]c增加46%。然而，[Ca2+]c的增加幅度小于呼吸性或代谢性碱中毒时的增加幅度。因此，低碳酸血症引起的脑血管收缩可能涉及Ins(1,4,5)P3的产生以及随之而来的[Ca2+]c升高。虽然Ins(1,
